1. Field of the Invention
The present invention relates to a light source unit and a projector that includes the light source unit.
2. Description of the Related Art
In these days, data projectors are used on many occasions as image projection units which project images including images of a screen and video images of a personal computer, as well as images based on image data which are stored in a memory card on to a screen. In these projectors, light emitted from a light source is collected on to a micromirror display element called a digital micromirror device (DMD) or a liquid crystal panel for projection of color images on to a screen.
Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made many developments and proposals on light source units which use light emitting diodes (LEDs), laser diodes (LD) or organic electroluminescent semiconductors.
For example, KOKAI (Japanese Unexamined Patent Publication) No. 2004-341105 (Patent Literature 1) proposes a light source unit that includes a light emitting wheel on which a luminescent material is laid in a circumferential direction and an ultraviolet light emitting diode. The light source unit proposed in Patent Literature 1 is configured so that ultraviolet light as an excitation light is shone on to the light emitting wheel from a rear side thereof to emit luminescent light from a front side of the light emitting wheel for use as light source light.
Then, in a light source unit for use in a projector, it is required that the light source unit can generate light having a wavelength band of red light, light having a wavelength band of green light and light having a wavelength band of blue light as the three primary colors of light. In a configuration that employs a light emitting wheel like the one described in KOKAI No. 2004-341105, it is possible to generate the three primary colors of light by laying a red luminescent material layer, a green luminescent material layer and a blue luminescent material layer in an end-to-end fashion in a circumferential direction.
In addition, KOKAI (Japanese Unexamined Patent Publication) No. 2011-013317 proposes a projector which employs alight source unit including a blue laser emitting device. In this light source unit, a laser beam in the blue wavelength band is emitted as diffuse light from a diffusing portion to be shone on to a DMD through a light source side optical system and so on. Then, light in the green wavelength band is emitted from a green luminescent material by making use of the laser beam in the blue wavelength band as excitation light and is then shone on to the DMD through the light source side optical system and so on. Further, light in the red wavelength band is emitted from a red light emitting diode and is then shone on to the DMD through the light source side optical system and so on.
The light source unit according to KOKAI No. 2004-341105 has a problem that there is caused a big difference in luminance between the red, green and blue light.
Additionally, the light source unit according to KOKAI No. 2011-013317 has a problem that it is difficult to increase the luminance of red light, and hence, it is difficult that the projector forms a bright projection image.